Soil Formation (Pedogenesis)- Definition, Factors, Process, Steps, Examples

Definition of Soil Formation

The process through which soil grows over time from weathered rock, organic matter, and other components in the environment is known as soil formation. This process involves the interaction of physical, chemical, and biological processes that transform basic materials into a complex, living environment that supports the growth of plants and other forms of life. Climate, terrain, vegetation, and human activity can all impact the rate and type of soil formation in a certain region. Soil formation is a long and ongoing process that can take hundreds or thousands of years to complete, and it is necessary for life on Earth to persist.

What is Pedogenesis?

Pedogenesis is the scientific term for soil formation. It refers to the complex process by which soils develop from the weathering and erosion of rocks and minerals, the decomposition of organic matter, and the accumulation of nutrients and other materials in the soil. Pedogenesis involves a combination of physical, chemical, and biological processes that interact over long periods of time to create distinct soil profiles with unique properties and characteristics. These soil profiles are often used by scientists to understand the history of a particular landscape, and they can provide important information about soil fertility, water-holding capacity, and other factors that are important for agriculture, forestry, and other land uses. Pedogenesis is a dynamic and ongoing process that is influenced by a wide range of factors, including climate, topography, vegetation, and human activities, and it is essential for supporting life on Earth.

Characteristics of Soil

• Texture: Soil texture refers to the size of mineral particles in the soil, such as sand, silt, and clay. Soil texture influences properties such as water-holding capacity, nutrient availability, and drainage.
• Structure: Soil structure refers to the arrangement of soil particles into aggregates or clumps, which can influence soil porosity, aeration, and water movement.
• Color: Soil color can vary depending on factors such as mineral content, organic matter content, and moisture level, and can provide clues about soil composition and properties.
• Organic matter content: Soil organic matter refers to the dead and decaying plant and animal material in the soil, and can contribute to soil fertility, structure, and nutrient cycling.
• pH: Soil pH is a measure of soil acidity or alkalinity, and can impact nutrient availability and plant growth.
• Nutrient content: Soil nutrients such as nitrogen, phosphorus, and potassium are essential for plant growth, and can influence soil fertility and productivity.
• Water-holding capacity: Soil water-holding capacity refers to the ability of soil to hold and release water, and can influence plant growth and drought resistance.
• Biological activity: Soil is home to a wide variety of living organisms such as bacteria, fungi, and insects, which can contribute to nutrient cycling, soil structure, and other aspects of soil health.

Principal Pedogenic Processes

A multitude of mechanisms contribute to the creation of soils. This is evidenced by the vast array of soil types classified by soil experts. On the other hand, we can say that there are five major pedogenic processes functioning on soils at the macro scale. These processes are laterization, podzolization, calcification, salinization, and gleization.

1. Laterization: Laterization is a frequent pedogenic phenomenon observed in tropical and subtropical soils. Rapid weathering of rocks and minerals is caused by high temperatures and heavy precipitation. Large quantities of water moving through the soil allow eluviation and leaching to occur. Almost all of the byproducts of weathering, relatively simple tiny compounds or nutrient ions, are removed from the soil profile by leaching if they are not absorbed by plants. Compounds of iron and aluminum are the two exceptions to this rule. Iron oxides impart the distinctive crimson hue to tropical soils. As a result of the net loss of base cations, heavy leaching also results in an acidic pH in these soils.
2. Podzolization: Podzolization is related with damp, chilly conditions at mid-latitudes and coniferous vegetation. Decomposition of pine litter and excessive summer precipitation produce a very acidic soil solution. This acidic soil solution increases eluviation and leaching processes, resulting in the removal of soluble base cations and aluminum and iron compounds from the A horizon. This procedure produces a sublayer in the A horizon that is formed of silica sand and is white to gray in hue.
3. Calcification: When evapotranspiration surpasses precipitation, calcification occurs due to the upward flow of dissolved alkaline salts from groundwater. At the same time, the passage of rain water causes the salts to travel downhill. The net effect is the deposition of translocated cations at the B horizon. In some instances, these deposits might produce a caliche-like layer. Calcium carbonate is the most prevalent component involved in this process. Calcification occurs frequently in prairie grasslands.
4. Salinization: Salinization is a process that resembles calcification in its operation. In contrast to calcification, salt deposition occurs at or very close to the soil surface. Salinization also occurs in significantly drier areas.
5. Gleization: Gleization is a pedogenic phenomenon resulting from inadequate drainage. This process is characterized by the buildup of organic matter in the top soil layers. Due to the chemical reduction of iron, the mineral layers in the lower horizons have a blue-gray hue.

Basic/Fundamental Pedogenic Processes

1. Humification

• Humification is the decomposition (transformation) of raw organic materials into humus.
• It is a highly complex process involving several creatures, including bacteria, fungus, actinomycetes, earthworms, and termites.
• There are two steps to the decomposition of organic matter: mineralization and humification. Mineralization is the metabolic breakdown of dead plant tissue by soil microbes into soluble organic compounds, mineral compounds, metal cations, and gases (CO2).
• During humification, soluble organic compounds polymerize and reform into insoluble big molecules. They make up the majority of soil humus and provide a location for cation retention.
• The other component of humus is polysaccharides, which are the gelatinous byproducts of microbial excreta that aid in soil aggregation.

2. Eluviation 

• Eluviation signifies “Washing away.” It is the elimination of components in suspension or solution by water percolating from upper to lower levels.
• Eluviation entails the mobilization and relocation of mobile elements, resulting in variations in texture.

3. Illuviation

• “illuviation” refers to the deposition of soil materials (removed from the eluvial horizon “E”) in the lower layer (or gain horizon with the property of stabilizing translocated clay components).
• This technique produces horizons known as illuvial horizons (B-horizon especially). All of these fundamental pedogenic processes interact to produce a variety of diverse soils on the earth’s surface.

4. Podzolization

• It is a soil formation process that results in the development of podzols and podzolic soils.
• It is the process of silica buildup and sesquioxide elimination.

5. laterization

• Some soils in the tropics are massively saturated with sesquioxides to the tune of 70 to 80 percent of the total mass, forming a cemented horizon that, when dried, becomes extremely brittle and brick-like.
• This process of soil formation is known as “laterization” or “lotozation,” as in the Malabar hills of Kerala.

6. Gleization

• gleization is a process of soil formation that results in the production of a glei (or gley) horizon in the lowest portion of the profile above the parent material as a result of poor drainage or waterlogged circumstances.
• These soils are known as “hydromorphic soils.” This procedure is frequently dependent on drainage characteristics rather than environment (heavy rainfall as in humid regions).

7. Salinization

• It is the accumulation of salts such as sulfates, chlorides of calcium, magnesium, sodium, and potassium in the form of a salinized (salic) horizon in soils.
• Saline soils are those with an ESP of less than 15 percent and a pH between 7 and 8.5. As in humid climates, precipitation is dependent on drainage characteristics.

8. Salonization Or Alkalization

• Under arid and semi-arid circumstances, the buildup of sodium ions on the exchange complex of clay to a concentration of >15% results in the production of sodic soils (solonetz).
• This happens when anions such as carbonates and bicarbonates dominate the soil.

9. Salodization Or Dealkalization

• This procedure involves the elimination of Na+ from exchange sites.
• The Na+ can be reduced by raising the Ca2+ or Mg2+ concentration in the water, followed by the improvement of drainage facilities.

Factors affecting Soil Formation

Soil formation is influenced by a variety of factors, both natural and human-induced. Some of the key factors that affect soil formation include:

• Parent material: Parent Material refers to the rocks and minerals from which soils are derived. These components may be generated from bedrock-residual sediment or sediment transferred to a region by wind, water, or glacier erosion. Pedogenesis is frequently accelerated on imported sediments because the weathering of source material is typically a lengthy process. Typically, soil texture, soil chemistry, and nutrient cycling are associated with the effect of parent material on pedogenesis.
• Climate: Climate has a crucial effect in the formation of soil. On a worldwide scale, there is a clear association between the major soil types and the major climatic kinds of the Koppen climatic classification system. At regional and local scales, climate influences soil formation less. In contrast, pedogenesis is significantly impacted by parent material, geography, vegetation, and time. Temperature and moisture are the two most critical climatic elements influencing soil formation. Warmth has a direct effect on the deterioration of bedrock into mineral particles. Temperature generally increases the rate of bedrock weathering. Temperature also affects soil microbial activity, the frequency and severity of soil chemical reactions, and plant growth rate. Moisture levels in the majority of soils are primarily determined by the amount of water added by precipitation minus the amount lost via evapotranspiration. When additions of water from precipitation exceed losses from evapotranspiration, soil moisture levels are often high. If evapotranspiration losses are greater than precipitation inputs, soil moisture levels tend to be low. A soil with abundant moisture facilitates the weathering of bedrock and sediments, chemical reactions, and plant growth. The availability of water also affects the pH of the soil and the decomposition of organic material.
• Topography: In general, topography impacts the formation of soil on a local or regional scale. Pedogenesis is primarily affected by the effect of topography on microclimate and drainage. Soils forming on moderate to gentle slopes are frequently better drained than soils in valley bottoms. A variety of pedogenic processes of illuviation and eluviation that are responsible for the formation of soil horizons are facilitated by adequate drainage. Under conditions of inadequate drainage, soils are typically immature. Because of erosion, steep topographic gradients hinder the growth of soils. Erosion can impede growth by continuously removing surface sediments. The microclimate of the soil is also influenced by geography. South-facing slopes in the Northern Hemisphere are often warmer and drier than north-facing slopes. Hence, the soils of the two regions differ in terms of depth, texture, biological activity, and evolution of the soil profile.
• Biological activity: The presence of plants, animals, and microorganisms can impact soil formation by affecting soil structure, nutrient cycling, and organic matter accumulation.
• Time: Time influences the temporal effects of all the aforementioned components. When a soil reaches maturity, numerous processes establish a stable state throughout time. In order to establish equilibrium, pedogenic processes in young soils are typically actively modified by negative and positive feedback mechanisms.
• Human activity: Human activities such as agriculture, deforestation, and urbanization can have significant impacts on soil formation by altering natural soil processes and introducing new materials and contaminants to the soil.
• Living Organisms: Organisms play an important part in pedogenesis processes like as organic matter buildup, profile mixing, and biogeochemical nutrient cycling. By nitrogen cycle, vegetation and soil are intimately connected under equilibrium conditions. The existence of animals and plants controls the cycling of nitrogen and carbon in soils nearly entirely. By decomposition and litterfall, organisms provide humus and nutrients to the soil, influencing its structure and fertility. Surface vegetation also protects the higher soil layers from erosion by binding the soil surface and slowing the movement of wind and water across the ground.

These factors can interact in complex ways to influence soil formation, and understanding their effects is essential for managing and conserving soil resources.

Soil Formation process or steps

Soil formation is a complex process that occurs over long periods of time and involves a combination of physical, chemical, and biological processes. Although the exact process can vary depending on factors such as climate, geology, and vegetation, there are some general steps involved in soil formation. These include:

1. Weathering: The process by which rocks and minerals are broken down into smaller particles by physical and chemical processes such as freezing and thawing, chemical reactions, and plant root growth.
2. Erosion: The movement of soil particles by water, wind, or gravity, which can transport them to other areas and contribute to the formation of new soils.
3. Deposition: The accumulation of soil particles in a particular location, which can be influenced by factors such as topography, vegetation, and climate.
4. Organic matter accumulation: The accumulation of organic matter from dead plants and animals, which can contribute to soil fertility and structure.
5. Soil mixing: The mixing of different types of soil, such as through the actions of burrowing animals or the movement of water, which can create new soil layers and change soil properties.
6. Soil development: The gradual development of distinct soil layers or horizons, each with its own unique properties and characteristics, such as texture, color, and nutrient content.
7. Soil profile formation: The accumulation of distinct soil horizons over time to create a soil profile, which can provide important information about the history and properties of the soil.

These steps can occur simultaneously or sequentially and can interact in complex ways to create the wide variety of soils found around the world. Soil formation is an ongoing process that can take hundreds or thousands of years to complete, and it is essential for supporting life on Earth.

Significance/Importance of Soil

Soil is a critical component of our planet’s ecosystem and plays a vital role in supporting life. Here are some of the key significance and importance of soil:

• Food production: Soil is the primary medium for plant growth, and provides the nutrients and water that are necessary for crops to grow. The vast majority of our food supply comes from plants grown in soil.
• Biodiversity: Soil is home to a wide variety of living organisms, from bacteria and fungi to insects and small mammals, which contribute to biodiversity and ecosystem health.
• Carbon storage: Soil is a significant carbon sink, storing large amounts of carbon in organic matter and helping to mitigate climate change.
• Water cycling: Soil plays a crucial role in the water cycle, helping to absorb and store water and release it slowly over time, reducing the risk of floods and droughts.
• Nutrient cycling: Soil plays a key role in the cycling of nutrients such as nitrogen, phosphorus, and potassium, which are essential for plant growth and ecosystem health.
• Cultural and historical significance: Soil has significant cultural and historical significance, playing a role in agriculture, architecture, art, and human settlement patterns.
• Economic importance: Soil provides the foundation for many economic activities, including agriculture, forestry, mining, and construction.
• Environmental protection: Soil can play a critical role in protecting the environment, filtering pollutants, and reducing erosion and sedimentation.

Significance/Importance of Pedogenesis

Pedogenesis, the process of soil formation, is crucial for the development and maintenance of soil resources. Here are some of the key significance and importance of pedogenesis:

• Soil formation: Pedogenesis is the process by which soil is formed from the weathering and decomposition of rocks and organic matter. Understanding the factors that influence soil formation can help us to manage and conserve soil resources more effectively.
• Soil fertility: Pedogenesis is a key determinant of soil fertility, influencing the availability of nutrients, water-holding capacity, and other factors that are essential for plant growth and crop productivity.
• Environmental protection: Understanding pedogenesis can help us to design and implement soil conservation practices that can reduce erosion, improve water quality, and protect natural habitats and ecosystems.
• Carbon sequestration: Pedogenesis can play a critical role in carbon sequestration, as soil can store large amounts of carbon in organic matter. Understanding pedogenesis can help us to develop strategies for managing soil resources that can mitigate climate change.
• Sustainable agriculture: Pedogenesis can provide insights into soil management practices that can promote sustainable agriculture, such as conservation tillage, crop rotation, and the use of cover crops.
• Historical significance: Pedogenesis has played a significant role in human history, from the development of agriculture to the construction of buildings and infrastructure. Understanding pedogenesis can help us to appreciate and preserve the cultural and historical significance of soil.

FAQ

References

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